1. Field of the Invention
The present invention relates to a copier, printer, facsimile apparatus or similar electrophotographic image forming apparatus and more particularly to a roller device for a contact type image transferring device.
2. Description of the Background Art
A contact type image transferring device is extensively used for an electrophotographic image forming apparatus because it does not produce nitrogen oxides or similar toxic components and because it is operable with a low voltage and therefore cost effective. These advantages are not achievable with a corona discharge type image transferring device. The contact type image transferring device includes a roller device including an image transfer roller. The image transfer roller is pressed against a photoconductive drum in such a manner as to be movable substantially perpendicularly to the axis of the drum. The roller rotates while absorbing the thickness of a paper sheet or similar recording medium being conveyed as well as the eccentricity of the roller and drum. For this purpose, compression springs exert a preselected load on bearings that support opposite ends of the roller. The roller must be replaced when it wears due to aging or is contaminated in order to maintain the expected image transferring ability and conveying ability.
Japanese Patent Laid-Open Publication Nos. 5-333721 and 9-138590, for example, each propose a semicircular bearing formed with an opening and simple means for preventing a shaft from slipping out of the bearing. Although this bearing may facilitate the replacement of an image transfer roller, carrier and toner particles, as well as other impurities, are apt to enter the bearing and produce noise while increasing resistance to rotation. While Japanese Patent Laid-Open Publication No. 11-93940 discloses a similar arrangement, it needs extra means for locking and unlocking a color that prevents the shaft of a roller from slipping cut.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-64279 and 2000-356217.
It is an object of the present invention to provide a roller device capable of facilitating the attachment and detachment of an image transfer roller with a simple configuration and accurately positioning the roller at a preselected position.
It is another object of the present invention to provide a roller device capable of cleaning the shaft of an image transfer roller over a long period of time and insuring reliable rotation of the roller.
It is a further object of the present invention to provide an image transferring device including the above roller device and an image forming apparatus including the image transferring device.
A roller device of the present invention includes a roller including a shaft, a bearing for rotatably supporting the shaft, a pressing device for pressing the bearing, and a lug protruding from the bearing in the axial direction of the roller. The pressing device is implemented as a pair of hook members deformable away from each other in.a direction perpendicular to the axis of the roller.
An image transferring device including the above roller device and an image forming apparatus including the image transferring device are also disclosed.